Using Entity Framework T4 Templates with System-Versioned Temporal Tables

Question

To resolve my error (shown below) I would like to know how to edit my Entity Framework T4 template so that it adds “HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed)” to the GENERATED ALWAYS AS ROW START/END columns of my Temporal Table in the POCO Configuration section of the auto-generated class like this:

Property(x => x.ValidFrom).HasColumnName(@"valid_from").HasColumnType("datetime2").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed);
Property(x => x.ValidTo).HasColumnName(@"valid_to").HasColumnType("datetime2").IsRequired().HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed);

I can manually add this (which resolves my error), but of course it's overwritten when I save the T4 template.

Error trying to insert a record: "Cannot insert an explicit value into a GENERATED ALWAYS column in table 'my_table’. Use INSERT with a column list to exclude the GENERATED ALWAYS column, or insert a DEFAULT into GENERATED ALWAYS column."

I saw this post, but it didn’t help (maybe it only works when using edmx files, or I didn’t understand the solution): Entity Framework not working with temporal table

Example of my Temporal Table:

CREATE TABLE [dbo].[my_table](
    [id] [int] IDENTITY(1,1) NOT NULL,
    [user_id] [int] NOT NULL,
    [valid_from] [datetime2](7) GENERATED ALWAYS AS ROW START NOT NULL,
    [valid_to] [datetime2](7) GENERATED ALWAYS AS ROW END NOT NULL,
 CONSTRAINT [PK_my_table] PRIMARY KEY CLUSTERED 
(
    [id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
    PERIOD FOR SYSTEM_TIME ([valid_from], [valid_to])
) ON [PRIMARY]
WITH
(
SYSTEM_VERSIONING = ON ( HISTORY_TABLE = [dbo].[my_table_history] )
)
GO
ALTER TABLE [dbo].[my_table] ADD  CONSTRAINT [DF_my_table_SysStart]  DEFAULT (sysutcdatetime()) FOR [valid_from]
GO
ALTER TABLE [dbo].[my_table] ADD  CONSTRAINT [DF_my_table_SysEnd]  DEFAULT (CONVERT([datetime2](7),'9999-12-31 23:59:59')) FOR [valid_to]
GO

Example code to insert a record:

var recordToCreate = new MyTable()
{
    UserId = info.UserId,
    ValidFrom = info.ValidFrom,
    ValidTo = info.ValidTo,
};
_context.MyTables.Add(recordToCreate);
_context.SaveChanges();

Answer 1

I figured it out. I had to edit the EF.Reverse.POCO.Core.ttinclude file, adding ‘IsGeneratedAlwaysType’ to a number of classes, methods and SQL queries. I basically added it everywhere I found ‘IsForeignKey’. I’ve pasted below the snippet of what I added to each section.

public class Column
{
    public bool IsGeneratedAlwaysType;

---

    private void SetupConfig()
    {
        else if (IsGeneratedAlwaysType)
        {
            if(Settings.UseDataAnnotations)
                DataAnnotations.Add("DatabaseGenerated(DatabaseGeneratedOption.Computed)");
            else
                databaseGeneratedOption = string.Format(".HasDatabaseGeneratedOption({0}DatabaseGeneratedOption.Computed)", schemaReference);
        }

---

    private static Column CreateColumn(IDataRecord rdr, Regex rxClean, Table table, Regex columnFilterExclude)
    { 
        var col = new Column
        {
            IsGeneratedAlwaysType = rdr["IsGeneratedAlwaysType"].ToString().Trim().ToLower() == "true",

---

private class SqlServerSchemaReader : SchemaReader
{
    private const string TableSQL = @"
    CAST(CASE WHEN COLUMNPROPERTY(OBJECT_ID(QUOTENAME(c.TABLE_SCHEMA) + '.' + QUOTENAME(c.TABLE_NAME)), c.COLUMN_NAME, 'GeneratedAlwaysType') > 0 THEN 1
         ELSE 0
       END AS BIT) AS IsGeneratedAlwaysType
    FROM    #Columns c

---

private const string SynonymTableSQLSetup = @"
        CAST(CASE WHEN COLUMNPROPERTY(OBJECT_ID(QUOTENAME(sc.NAME) + '.' + QUOTENAME(o.NAME)), c.NAME, 'GeneratedAlwaysType') > 0 THEN 1
                  ELSE 0
             END AS BIT) AS IsGeneratedAlwaysType
        INTO    #SynonymDetails
        FROM    sys.synonyms sn

---

INSERT INTO #SynonymDetails (SchemaName, TableName, TableType, Ordinal, ColumnName, IsNullable, TypeName, [MaxLength], [Precision],
                            [Default], DateTimePrecision, Scale, IsIdentity, IsStoreGenerated, PrimaryKey, PrimaryKeyOrdinal, IsForeignKey, IsGeneratedAlwaysType)

---

CAST(CASE WHEN COLUMNPROPERTY(st.base_object_id, c.NAME, ''GeneratedAlwaysType'') > 0 THEN 1
                ELSE 0
            END AS BIT) AS IsGeneratedAlwaysType
FROM    #SynonymTargets st
    INNER JOIN sys.columns c

---

        private const string SynonymTableSQL = @"
SELECT SchemaName, TableName, TableType, Ordinal, ColumnName, IsNullable, TypeName, [MaxLength], [Precision],
    [Default], DateTimePrecision, Scale, IsIdentity, IsStoreGenerated, PrimaryKey, PrimaryKeyOrdinal, IsForeignKey, IsGeneratedAlwaysType FROM #SynonymDetails";

---

        private const string TableSQLCE = @"
0 as IsGeneratedAlwaysType
FROM    INFORMATION_SCHEMA.COLUMNS c